Since the first practical applications of the Otto and Diesel cycles in internal combustion engines, engineers the world over have struggled to improve the power-to-weight ratio and/or fuel efficiency of such engines. Frequently, designers have considered alternatives or modifications to the standard four-stroke engine cycles. For example, in small engines a two-stroke cycle may be used to increase the power-to-weight ratio. However, the two-stroke cycle actually tends to reduce fuel efficiency and also tends to produce undesirable chemical byproducts of partial fuel and lubrication oil combustion.
As one example of prior art attempts to improve the internal combustion engine, U.S. Pat. No. 6,209,495 discloses a two stroke compound engine that has a pair of horizontally opposed piston cylinder assemblies extending along a common axis therein. Each piston cylinder assembly includes a piston, a combustion chamber and respective inlet and exhaust valves. A pair of connecting rods extending along the common axis connect the respective pistons to a crank extending from a rotary housing. The rotary housing is rotatably mounted within the engine and includes an output shaft extending co-axially therefrom. A fixed ring gear is mounted co-axially about the rotary housing along an axis extending perpendicularly to the common axis. A planetary gear mounted on the crank meshes with the ring gear for rotating the rotatable housing in response to reciprocation of the pistons. A pair of combustors are mounted on exhaust ports of the respective piston assemblies for further combusting exhaust from the combustion chambers by mixing exhaust with cooling air and additional fuel. A turbine recovers power from the combustion within the combustors. The turbine is connected to the output shaft by a gearing mechanism and an overrunning clutch mechanism.
As another example selected from the thousands of modifications proposed to the well-known four-stroke engine cycle, U.S. Pat. No. 6,722,322 discloses an internal combustion engine including an engine cylinder that includes a cylinder cavity with first and second cylinder heads. A single piston member is slidably movable within the cylinder cavity between the first and second heads to partition the cavity into first and second combustion chambers, which are in alternate combustion in normal engine operation.
As yet another example of previous efforts, U.S. Pat. No. 4,934,344 discloses an internal combustion engine with a modified four stroke cycle which takes place during a single revolution of a crankshaft having first and second cam lobes, which drive a reciprocating piston via a connecting rod pivotally connected to a guide link driven by a camshaft. In the modified four stroke cycle of the '344 patent, the single piston moves through short duration compression and power strokes, then through relatively long duration exhaust and intake strokes.